1. Field of the Invention
This invention relates to static neutralizers for roll-type dispensers of pressure-sensitive and adhesive tape prior to application thereof in strip form of selective lengths to the intended article or parts. More particularly, this invention concerns an induction or passive static discharging means for dispensers delivering adhesive as well as non-adhesive backed tapes and film.
When thin film plastic tapes, including cellophane, polyesters, polyethylene, polypropylene, vinyls and the like are radially peeled from an underlying roll on which they are coiled, preparatory to adhesive placement in strip form upon an article surface or in a second smaller coil wrapped about an object, a static charge is triboelectrically developed on the free end of the tape as a consequence of the separation of the two surfaces previously in intimate contact with each other. This results in one of the surfaces (on a tape section now peeled away but theretofore in abutment) assuming a charge of one polarity while the other surface (on a tape portion still coiled but just bared by the stripped away-section) becomes charged to the opposite polarity.
This problem is especially exaggerated in the case of very thin film polyester pressure sensitive tape (for example, "Mylar", a product of E. I. DuPont de Nemours), where thickness is one mil or less, when it is almost impossible to manipulate statically charged strips being dispensed. Such tape becomes so highly charged to the extent that sections are incontrollably attracted to or repelled from adjacent bodies and are characterized by a tendency to stick to themselves, to the roll from which they were recently attached and/or to cling to the user's hands. Since strips of these tapes are dispensed from rolls as a matter of course in the electrical industry, for example in wrapping components, in offices, by artists and decorators, as well as by the general public, it is apparent static charge conditions in regard to tape dispensers are quite significant.
Elimination of static electricity during manufacture of the tape or upon formation of the tape into rolled-up coils does not alleviate the problem because during dispensation from the roll, the triboelectric or frictional peeling effect produces a reecharging of the tape's drawn off free end, the charge being opposite in polarity to that on the outer coil surface from which the separated portion was drawn. The manifestation of the charging indicia is set forth in FIG. 1.
2. Prior art
In U.S. Pat. No. 3,636,408, there is shown a tape dispenser in combination with a static neutralizer in which a free end of the tape is drawn past a plurality of electrical conductors, such as brushes, transversely disposed across one or both sides thereof and connected to electrical ground. An example of this prior art system is shown in FIG. 2. If a grounding mechanism were not used in this patented system, the brushes would "float" and charge up themselves, thus defining a capacitance preventing further current flow.
U.S. Pat. No. 2,264,683 employs a radioactive substance in the dispenser adjacent the free end of the tape to effect neutralization of the static charges by means of alpha rays. The disadvantage of this approach is the limited life of the radioactive substance in addition to the restrictions imposed by the NRC upon radioactive materials, the latter preventing the usage of such dispensers by the general public.
U.S. Pat. No. 3,128,492 shows a device for neutralizing film by impinging ions of both polarities upon one or both surfaces by means of high voltage static eliminators located within the housing and coupled to a power cord for insertion in a line receptacle. Still another type of neutralizer presently marketed employs a high voltage air ionizer mounted within the base of the tape dispenser wherein two emitters, one of each polarity, directs air ions generated by corona discharge against the film. The problems associated with each of these latter approaches are the large dispenser size to accommodate a power supply, the need to plug into a line power outlet, the proximity of high voltage and very high relative cost.